shared: Fix free() of unallocated response_store

When a message cannot be deserialized, response_store is unallocated,
however we're still trying to free it in end:, this commit fixes
this behaviour.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
Fix the minimum size again.

Incorrect assumption being made about size, we're only interested in
the size of a buxton *control* length, which is a uint32_t and a size_t
The rest is part of a buxton message itself.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>